1. Field of the Invention
This invention relates generally to apparatus and methods for isolating an upper portion of a well bore from a lower portion of a well bore, and more particularly, but not by way of limitation, to methods of gravel packing a selected zone of a well bore of an oil or gas well and of isolating said zone from a portion of the well bore located thereabove upon completion of the gravel packing operation.
2. Description of the Prior Art
One operation sometimes performed during the completion of an oil or gas well is the packing of a selected zone of the well bore, adjacent a producing subsurface formation, with particulate material. Such operations are generally referred to as "gravel packing". The term "gravel packing" is, as will be understood by those skilled in the art, defined for the purposes of this invention as including the packing of the selected zone of the well bore with any particulate material even though that particulate material may be of such a size that it would be referred to in lay terms as sand rather than gravel. This particulate material is carried down to the zone to be gravel packed in a slurry of liquid and particulate material, and the slurry is squeezed into the selected zone until the zone is packed substantially as densely as is possible with the particulate material.
One particular problem which has been encountered with prior art gravel packing apparatus and methods is that upon completion of the gravel packing operation, when the tubing string which conducts the slurry to the zone is withdrawn from an upper annular packer defining the upper end of the zone, the subsurface formation communicated with the gravel packed zone is thereby communicated with the portion of the well bore located above the upper packer. Thus, if there is a pressure differential between the producing zone and the well bore located thereabove, kicks or blowouts may occur since the producing zone is communicated with the well bore.
Two particular prior art methods and apparatus for performing gravel packing operations are illustrated in FIGS. 1-7 and in FIGS. 8-12, respectively. Those prior art methods will now be described with reference to those figures.
FIGS. 1-5 schematically illustrate five sequential steps in the performing of what is generally referred to as a "high density" gravel packing operation.
FIG. 1 schematically illustrates, in elevation, a well having a well bore 10 defined by a well casing 12. The well casing 12 extends from an upper end 14 at a ground surface 16 to a lower end 18. Located below lower end 18 is the blind lower end of the uncased well bore which is generally referred to as a rathole 20.
The well intersects a subsurface hydrocarbon producing formation 22 and the well bore 10 is communicated therewith by a plurality of casing perforations 24.
Generally, the first step which is involved in constructing a gravel packing apparatus in a well and performing the gravel packing operation is to lower a lower packer means 26 into the well bore 10 and set the packer means 26 in the well bore 10 at a lower end of the zone of the well bore which is to be gravel packed. The lower packer means 26 is generally referred to as a sump packer and it may be run and set by an electric line as will be understood by those skilled in the art. The sump packer 26 generally includes a packer body 28 having a longitudinal passageway disposed therethrough and having an inflatable annular packing element 30 disposed thereabout for sealing an annulus between the packer body 28 and the well bore 10.
Referring now to FIG. 2, the resulting apparatus from the next series of steps is there illustrated. First, an upper packer means 32 is made up on a lower end of a supply tubing string 34. Upper packer means 32 generally includes a packer body 36 having a lower packer body extension 40, and includes an inflatable packing element 42 for sealing between packer body 36 and well bore 10. Connected to a lower end of packer body 36 is an intermediate tubing 44 which is generally referred to as a "blank" or "blank tubing". Connected to a lower end of the blank tubing 44 is a production screen means 46 which communicates a zone 48 of well bore 12 defined between upper and lower packers 32 and 26 with an interior of blank tubing 44, and thus with a longitudinal passageway disposed through packer body 36 of upper packer 32. Connected to a lower end of production screen means 46 is a lower tubing 47.
The upper packer 32, blank tubing 44, screen means 46, and lower tubing 47 are made up upon supply tubing string 34 before the supply tubing string 34 is lowered into the well bore 10. Then, the supply tubing string 34 with the described attached apparatus is lowered into the well bore 10 until the upper packer means 32 is located at an elevation at which it is desired to define the upper end of the zone 48 to be gravel packed. Then the upper packer means 32 is set in the well bore 10 as shown in FIG. 2 to seal the annulus between the packer body 36 and the well bore 10. Generally, the lower tubing 47 will be sealingly received within the longitudinal passageway of packer body 28 of lower packer means 26.
Next, the slurry containing the particulate material is pumped down the interior of supply tubing string 34. Initially, the fluid previously present in the supply tubing string 34 is circulated out an upper port means 50 associated with a running tool 60 attached to tubing string 34 and as indicated by arrows 52, into an annulus between supply tubing string 34 and well bore 10 above upper packer means 32. This procedure continues until the slurry containing the particulate material is located a short distance above the upper packer means 32. This procedure is known in the art as "spotting" the gravel slurry. This spotting procedure is generally performed with the supply tubing string 34 held in tension so as to hold open the port means 50.
As will be understood by those skilled in the art, there is connected to the lower end of tubing string 34 the running tool 60 (see FIG. 4) which is disposed within the longitudinal passageway of packer body 36, and the port means 50 and other ports to be discussed below, are generally associated with both the packer body 36 and the running tool 60. Thus, manipulation of the tubing string 34 and the connected running tool 60 is generally performed to produce predetermined relative movements between the running tool 60 and the packer body 36 to open and close various ports located therein and to operate various other components of the packer body 36 or associated therewith as is further described below.
After the spotting operation has been completed, weight is set down upon the tubing string 34 to close the upper port means 50 and to open a lower port means 54 associated with lower packer extension 40. This lower port means 54 is communicated with the supply tubing string 34 so that the slurry containing particulate material may then be introduced into the zone 48 through the lower port means 54.
This is illustrated in FIG. 3 where the arrows 56 represent the flow path of the particulate material down the tubing string 34, then through the packer body 36, then out the lower port means 54 into the zone 48. The slurry containing particulate material is squeezed into the zone 48 and fluid therefrom is squeezed out of the slurry and may flow out through the perforations 24 leaving the zone 48 densely packed with particulate material as schematically represented by the particles 58.
When the zone 48 is completely packed with particulate material 58, as schematically represented in FIG. 3, the supply tubing string 34 is withdrawn from packer body 36 of upper packer means 32 and is retrieved up to the ground surface 16. FIG. 4 schematically represents the supply tubing string 34 after it has been withdrawn from upper packer means 32 and as it is being retrieved to the ground surface 16. Schematically represented on the lower end of tubing string 34 is the running tool 60 previously referred to. As the running tool 60 is withdrawn from packer means 32 it closes lower port means 54.
During the operation illustrated in FIG. 4, the subsurface formation 22 is communicated with the zone 48 through the perforations 24 and with an interior of blank tubing 44 through production screen means 46. The interior of blank tubing 44 is communicated with the longitudinal passageway disposed through packer body 36 and is thus communicated with the well bore 10 located above upper packer means 32. Thus, if there is a pressure differential between the subsurface formation 22 and the well bore 10, there is the possibility of a kick or blowout occurring wherein fluid would flow upwardly through screen 46, blank tubing 44, packer body 36, and upper portion of well bore 10 in an uncontrolled manner. Similar problems can occur if there is a second subsurface formation located above upper packer 32 which is also communicated with the well bore 10 thus allowing communication between two previously separate subsurface formations. As will be understood by those skilled in the art, numerous problems can occur in such a situation where a subsurface formation containing fluid under pressure is not controllably contained by the oil well equipment.
After the supply tubing 34 has been retrieved, a production tubing string 62 is lowered into the well and connected to upper packer body 36 so that an interior of production tubing 62 is communicated through packer body 36, blank tubing 44, and production screen means 46, with the gravel packed zone 48 and thus with the subsurface producing formation 22 through the perforations 24 in the well casing 12. Then, the oil or gas from subsurface formation 22 may be produced upwardly through production tubing string 62 as indicated by arrows 64.
The problem of kicks or blowouts occuring between the gravel packed zone 48 and the well bore 10 located above upper packer means 32 is present during the period of time represented in FIG. 4 wherein the longitudinal passageway through the packer body 36 of upper packer means 32 is communicated with the well bore 10 above the packer means 32 and with zone 48.
The prior art has included some apparatus and methods for blocking that longitudinal passageway of upper packer body 36. These methods have required that after the supply tubing string 34 is retrieved, a plug means of a type generally referred to as a "cast iron bridge plug" is lowered either on an electric line or with a tool string into the well bore and through the packer means 36 into the blank tubing 44. Then the cast iron bridge plug is set within the blank tubing 44 either by electrical means or by manipulation of a tool string.
This prior art method of isolating the gravel packed zone 48 from the well bore 10 above upper packer means 32 is illustrated with reference to FIGS. 6 and 7.
In order to isolate zone 48 from the well bore 10 with prior art methods, the blank tubing 44 is initially made up with an adapter 66 located therein which includes, extending downward therefrom, a relatively short tubular section 68 which is concentrically received within the blank tubing 44.
Then, after the procedures illustrated and described with reference to FIG. 4 are completed, a cast iron bridge plug 70 is lowered into the inner tubing section 68 on an electric line 72 from the ground surface 16 and is set in the inner tubing section 68 by electrical means. Also, as previously mentioned, the cast iron bridge plug 70 may be set with a mechanical string in place of the electric line 72.
It is apparent from this description that even with this prior art method of isolating gravel packed zone 48 from the well bore 10 located above upper packer means 32, a period of time must exist between the time when the supply tubing string 34 is withdrawn from packer body 36 and the time at which the cast iron bridge plug 70 has been lowered on the electric line 72 and set within the inner tubing 68. Thus, this prior art method does not completely avoid the dangers present due to kicks and blowouts from pressure within subsurface formation 22 since the subsurface formation 22 is still communicated with the well bore 10 above upper packer means 32 for a substantial period of time during which the supply tubing string 34 is retrieved from the well bore 10 and during which the electric line 72 is lowering the bridge plug 70 into the well bore and into the concentric inner tubing 68 within which it is to be set.
Additionally, when it is desired to produce fluids from the subsurface formation 22 with the apparatus illustrated in FIG. 6, it is necessary to perforate the inner concentric tubing section 68 above the cast iron bridge plug 70 thus allowing the fluids to be produced in a manner illustrated in FIG. 7. The arrows 73 illustrate the flow of fluid from formation 22, through perforations 24, into production screen means 46, up through blank tubing 44 and an annular space between blank tubing 44 and inner concentric tubing 68, to an elevation above cast iron bridge plug 70, then through the perforations just described in the inner concentric tubing 68 into the inner concentric tubing 68, then up through the packer body 36 and the production tubing string 62. As will be understood by those skilled in the art, with the procedure of FIGS. 6 and 7 there is often considerable difficulty in creating the necessary perforations in the inner concentric tubing 68.
Referring now to FIGS. 8-12, five sequential illustrations are shown of a second type of prior art gravel packing apparatus and method, which is generally used to perform what is known as a "circulating pack" gravel packing operation. The circulating pack operation is generally utilized where the length of the zone to be packed is greater than thirty feet. Where the length of the zone to be packed is less than thirty feet, the high density gravel packing method of FIGS. 1-5 is generally used. When the length of the zone to be packed is greater than thirty feet, it has been experienced that problems occur in completely filling the zone with particulate material, particularly at its lower extremities, and thus the circulating pack method described below is preferable.
As shown in FIG. 8, the circulating pack method begins in the same manner as did the high density packing method by setting a lower sump packer 26 within the well bore 10 by means of an electric line.
Referring now to FIG. 9, it is seen that the apparatus made up on the lower end of supply tubing string 34 is different for the circulating pack method. With the circulating pack method there is additional apparatus connected to the lower end of production screen means 46, and additional apparatus is connected to the lower end of the running tool disposed in packer body 36 and connected to supply tubing string 34.
A seal bore nipple 74 is connected to a lower end of production screen means 46. A tell tail screen 76 is connected to a lower end of seal bore nipple 74. The lower tubing 47 is connected to a lower end of tell tail screen 76.
Connected to a lower end of the running tool disposed within the longitudinal passageway of packer body 36 of upper packer means 32 is a wash pipe 78, a lower end of which is sealingly received within an inner bore of seal bore nipple 74 and the interior of which communicates with the interior of the tell tail screen means 76.
The apparatus just described is made up to the supply tubing string 34 before the supply tubing string 34 is lowered into the well bore 10. Then the supply tubing string and attached apparatus is lowered into the well bore 10 until the upper packer means 32 is located at an elevation at which it is desired to define the upper end of the zone 48 to be gravel packed. Then the upper packer means 32 is set in the well bore 10 to seal between the packer body 36 and the well bore 10.
Generally, when the upper packer means 32 is set within the well bore 10, the lower tubing 47 is sealingly received within packer body 28 of lower packer means 26.
The running tool utilized in circulating pack methods is generally referred to by those skilled in the art as a "crossover running tool". This crossover running tool in association with the packer body 36 operates such that when the supply tubing string 34 is in tension, the interior of supply tubing string 34 is communicated with lower port means 54 of packer body 36 of upper packer means 32. Thus, the slurry flows down supply tubing 34 out the lower port means 54 into the zone 48. The tell tail screen means 76 is, however, at the same time communicated through the wash pipe 78 and through the upper port means 50 of the running tool with the well bore 10 above upper packer means 32, so that the slurry flows downwardly through zone 48 toward the tell tail screen 76 since the pressure at tell tail screen 76 is less than the pressure required to force the fluid out into the subsurface formation 22. The particulate material 58 thus initially concentrates in the lower extremity of the zone 48 and fluid from the slurry flows through the tell tail screen means 76, up through the wash pipe 78, then out the upper port means 50 into the well bore 10 above upper packer means 32. Since the zone 48 is full of fluid there will be some particulate material 58 throughout the zone, but it will initially concentrate at the lower end of zone 48. The lower end of zone 48 will become relatively densely packed with particulate material and when an upper level 80 of this densely packed portion of zone 48 reaches the level of tell tail screen means 76 it will be apparent at the surface 16 due to an increase in pressure necessary to force additional slurry material into zone 48.
At this time, the weight of the tubing string 34 is set down upon the upper packer means 32, thus closing the upper port means 50 to prevent further circulation of fluid from the slurry. The lower port means 54 remains open as illustrated in FIG. 10 and additional slurry is then squeezed into the zone 48 to densely fill the remainder of the zone 48 with particulate material 58 and the fluid from the slurry is squeezed out of the zone 48 through the perforations 24 into the subsurface formation 22.
After the zone 48 is completely packed with particulate material as illustrated in FIG. 10, the supply tubing string 34 and attached crossover running tool 82 and wash pipe 78 are disconnected from upper packer means 32 and withdrawn therefrom, and are retrieved to the ground surface 16 as illustrated in FIG. 11. As the running tool 82 is withdrawn it closes lower port means 54.
During the operation illustrated in FIG. 11, it is apparent that subsurface formation 22 is communicated through the perforations 24 with the zone 48, and through the production screen means 46, the blank tubing 44, and the longitudinal passageway of packer body 36, with the well bore 10 above upper packer means 32. Thus, it is apparent that the problem of kicks and blowouts may occur, just as is possible with the high density gravel packing method at the similar point illustrated in FIG. 4.
Then, the production tubing string 62 is lowered into connection with the upper packer means 32 to produce fluids from subsurface formation 22 through perforations 24, production screen means 46, blank tubing 44, and the packer body 36.
With the circulating pack apparatus and methods of FIGS. 8-12, the prior art has also included the use of an isolation means similar to that illustrated in FIGS. 6 and 7, wherein an inner concentric tubing is run in place with the blank tubing 44 and, subsequent to the withdrawal of the supply tubing 34 illustrated in FIG. 11, a cast iron bridge plug such as bridge plug 70 of FIGS. 6 and 7 can then be run on an electric line or on a mechanical string and set within the blank tubing 44.
The apparatus and methods described above with reference to FIGS. 1-12 are all a part of the prior art. It is seen that although the prior art includes apparatus and methods for performing gravel packing operations, and although the danger of allowing communication between the gravel packed zone 48 and the well bore 10 above the upper packer means 32 subsequent to the withdrawal of supply tubing string 34 and prior to the connection of production tubing string 62 has been known, the prior art has not included any apparatus or methods for isolating gravel packed zone 48 from the well bore 10 located thereabove prior to the withdrawal of the supply tubing string 34 from the upper packer means 32.